Hollow Cylinder Specimens Research Articles

A novel mirror-assisted method for full-field vibration measurement of a hollow cylinder using a three-dimensional continuously scanning laser Doppler vibrometer system

A novel general-purpose three-dimensional (3D) continuously scanning laser Doppler vibrometer (CSLDV) system was recently developed by the authors to measure 3D vibration of a structure with a curved surface. As a non-contact system, it can avoid the mass-loading problem in 3D vibration measurement using triaxial accelerometers. In previous studies, the 3D CSLDV system was used to measure 3D full-field vibration of a turbine blade with a curved surface and identify its operating deflection shapes (ODSs) and mode shapes. The 3D CSLDV system had the same level of accuracy as that with a commercial 3D scanning laser Doppler vibrometer system, but can measure many more points in much less time than the latter. However, the 3D CSLDV system can be limited by its field of view, which is a common problem for optical-based measurement devices. Moving the 3D CSLDV system to different positions to measure different parts of a test structure is not practical during 3D CSLDV measurement, since the system has to be re-calibrated once it has been moved, which can be time-consuming and introduce measurement errors. This work proposes a novel mirror-assisted testing methodology for 3D CSLDV measurement that aims to measure vibration of difficult-to-access areas of a structure without moving the 3D CSLDV system during the test, and stitch ODSs of its different parts together to obtain its panoramic 3D ODSs. The proposed methodology includes a novel scan trajectory design method that uses virtual areas of the structure behind the mirror to conduct continuous and synchronous scanning of three laser spots, and a novel velocity transformation method that uses virtual positions of three laser heads behind the mirror to stitch ODSs of different parts of the structure together. To demonstrate the proposed methodology, 3D CSLDV measurement is conducted on an aluminum hollow cylinder specimen, which has difficult-to-access areas such as its side and back surfaces, with the assistance of the mirror to obtain its panoramic 3D ODSs corresponding to its first two modes. Comparison between identified ODSs of the hollow cylinder specimen from the experiment and mode shapes from its finite element model is made and modal assurance criterion values are larger than 0.98.

Novel Method for Characterizing the Mechanical Properties of the Cement Sheath Based on Hollow-Cylinder Specimen and Multiaxial Load Tests

Summary Mechanical properties such as Young's modulus, Poisson's ratio, and strength are important parameters for evaluating the cement sheath integrity. However, the current triaxial testing methods for the mechanical properties of intact-cylinder cement specimens ignore the “ring” shape of the wellbore cement sheath and its nonuniform 3D stress distribution, which may lead to deviations from the actual mechanical properties of the wellbore cement sheath that can affect the theoretical analysis results. In this study, we designed a hollow-cylinder cement specimen to address the aforementioned conditions and conducted uni, tri, and multiaxial compression tests to analyze the differences in the deformation, damage, and mechanical failure of the hollow- and intact-cylinder cement specimens. It was found that under the same confining pressure, the Young’s modulus of the hollow-cylinder cement specimen with hole pressure was approximately 1.2 times that of the intact-cylinder cement specimen; however, the difference in Poisson’s ratio was not significant. The uniformity of the radial and circumferential stress distributions in the hollow-cylinder cement specimens was the main factor affecting the volumetric strain curves and the damage threshold. Under tri and multiaxial compression conditions, the deviatoric stress of the hollow-cylinder cement specimens was higher than that of the intact-cylinder cement specimens. Compared with the Mohr-Coulomb criterion, the twin-shear unified strength theory can more accurately reflect the relationships between the radial, circumferential, and axial stresses and the strength of the hollow-cylinder cement specimens. Through a failure test of the cement sheath based on a self-developed wellbore simulation device, it was verified that the mechanical properties of the hollow-cylinder cement specimens can better reflect the failure law of the wellbore cement sheath compared with intact-cylinder cement specimens. The findings of this study can contribute to the understanding of the mechanical behavior of wellbore cement sheaths.

Consideration of Fatigue Evaluation of SUS316 and SUS430 Steels under Multiaxial Stresses Combined Internal Pressure and Axial Load using Hollow Cylinder Specimen

This study focuses on discussing fatigue life evaluation method of SUS316 and SUS430 steels under wide ranged proportional multiaxial loading conditions. Fatigue tests under 7 types of loading path which are combined axial stress and inner pressure were carried out using hollow cylinder specimens at room temperature. It has been considered that the proportional loading does not cause additional hardening, however this study shows that the complex loading path causes additional hardening without principal direction change of stress and strain in a cycle. The Itoh-Sakane model which evaluates loading and lives under non-proportional multiaxial fatigue by only considering the maximum and the minimum principal stress or strain and their principal directions. However, this model is also needed to consider middle principal stress because change of the middle principal stress influence fatigue life under current loading paths. Therefore, the Itoh-Sakane model was modified to evaluation fatigue life of SUS316 and SUS430 under combined internal pressure and axial loading conditions.

Fatigue strength of adhesively butt-bonded hollow cylinders under multiaxial loading with constant and variable amplitudes

Adhesive bonding is commonly used in the manufacturing of vehicle bodies. A bond-line has the advantage that the joined flanges are stressed homogenously compared to a conventional spot-welded design. In addition, the bond-line provides a higher stiffness and better damping behavior. There exists still quite some uncertainty in the fatigue assessment of adhesively bonded joints due to a lack of reliable assessment approaches. This is especially true for the case of more complex in-service loading conditions as variable amplitude and multiaxial loading. For example, the experimentally determined actual damage sum in the literature shows a high scatter and is well below the theoretical value of one proposed by Palmgren-Miner. This uncertainty is typically countered by an over-dimensioning of the bond.In order to identify the fatigue strength behavior under constant and variable, multiaxial loading, fatigue tests on adhesively butt-bonded double hollow cylinder specimens with a thickness of the bonding of 0.3 mm have been performed under load control. The endurable damage sums according to the Palmgren-Miner hypothesis with a modified slope after the knee point of the Woehler line are determined and compared to data from the literature, they are significantly lower than Dth = 1. Non-proportional multiaxial loading (ϕ = 90°) does not reduce the fatigue life compared to proportional (ϕ = 0°).

Fatigue Property of Additively Manufactured Ti-6Al-4V under Nonproportional Multiaxial Loading

The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investigated under proportional and nonproportional multiaxial loading. The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments, at room temperature in air. Two fatigue tests were conducted: one for proportional loading and one for nonproportional loading. The proportional loading was represented by a push-pull strain path (PP) and the nonproportional loading by a circle strain path (CI). The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects. However, the sizes of the defects were measured, and the defects were found not to cause a reduction in fatigue strength above a critical size. The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths. Different fracture patterns were recognized for each strain paths; however, both showed retention of the crack propagation, despite the presence of numerous defects, probably because of the interaction of the defects. The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components.

Suitability of roughness parameters for the interlaminar strength prediction of mechanically interlocked polymer-metal-interfaces

The interlaminar strength of mechanically interlocked polymer-metal-interfaces strongly depends on the metal surface topography. Hence, this contribution assesses standardized surface roughness parameters as well as fractal dimension for interlaminar strength prediction of EN AW-6082/polyamide 6 polymer-metal-hybrids. Seven different metal surface topographies generated by mechanical blasting, alkaline etching, thermal spraying as well as laser structuring are investigated. Interlaminar strength testing is carried out with regard to tensile and shear strength using butt-bonded hollow cylinder specimens. The surface roughness profiles are recorded with a tactile stylus profiler. The fractal dimension of the metal surface is derived from cross-sectional images. The measured interlaminar strength values show good correlation to the fractal dimension, moderate correlation to the root mean square slope of the surface roughness profile and no correlation to surface roughness height parameters.

Can Heating Induce Borehole Closure?

The current study shows that heating a cased borehole in low-permeability shale rock can induce plastic deformation, leading to the closure of the casing annulus and decreasing annulus connectivity. The thermally induced borehole closure is interesting for the field operation of plug and abandonment (P&A), as it potentially saves operation cost and time by avoiding cutting casing and cementing. Lab experiments and numerical simulations are implemented to investigate the thermally induced borehole closure. Pierre shale and a field shale are tested. The lab experiments are performed by heating the borehole wall in a 10-cm-OD hollow cylinder specimen. Here, a novel experimental setup is applied, allowing for measuring temperature and pore pressure at different radii inside the specimen. Both the experimental data and the post-test CT images of the rock samples indicate the rock failure by borehole heating, and under certain conditions, heating results in an annulus closure. The decrease of hydraulic conductivity through the casing annulus is observed, but this decrease is not enough to form the hydraulic-sealed annulus barrier, based on the results obtained so far. Lab-scale finite-element simulations aim to match the lab results to obtain poro-elastoplastic parameters. Then the field-scale simulations assess the formation of shale barriers by heating in field scenarios. Overall, (i) the lab experiments show that heating a borehole can increase the pore pressure in shale and hence induce rock failure; (ii) the numerical simulations match the experimental results reasonably well and indicate that the heating-induced borehole closure can sufficiently seal the casing annulus in the field-scale simulation.

Investigation of fatigue strength under wide-ranged biaxial stress for two types of stainless steel using a thin-walled hollow cylinder specimen

Stress-controlled multiaxial fatigue tests were carried out by using hollow cylindrical specimens of type 430 and type 316 stainless steel at room temperature. A recently developed fatigue testing machine, which can apply push-pull loading and inner pressure to the specimen was used. By combining axial and hoop stresses, a pull, an inner-pressure, a push-pull, an equi-biaxial, a square, an LT, and an LC-shape cyclic loading were employed. Fatigue lives of two steel types using Itoh-Sakane (I-S) and Fatemi-Socie models were compared. Two models should be more effective if the effect of cyclic hardening is clarified.

Effect of Metal Surface Topography on the Interlaminar Shear and Tensile Strength of Aluminum/Polyamide 6 Polymer-Metal-Hybrids.

Mechanical interlocking has been proven to be an effective bonding mechanism for dissimilar material groups like polymers and metals. Therefore, this contribution assesses several surface pretreatments for the metallic adherent. Blasting, etching, combined blasting and etching, thermal spraying, and laser structuring processes are investigated with regard to the achievable interlaminar strength and the corresponding surface roughness parameters. The experiments are carried out on EN AW-6082/polyamide 6 polymer-metal-hybrids, utilizing a novel butt-bonded hollow cylinder specimen geometry for determining the shear and tensile strength. The experimental results indicate that the surface roughness slope has a major impact on the interlaminar strength. A laser-generated pin structure is found to provide the best mechanical performance as well as the highest surface slope of all investigated structuring methods.

Fatigue Life Properties of Stainless Steels in Wide Ranged Biaxial Stress State

Multiaxial fatigue tests consisting of push-pull loading and cyclic inner pressure were carried out using hollow cylinder specimens of type 430 stainless and type 316 stainless steels at room temperature. 7 types of cyclic loading paths were employed by combining axial and hoop stresses: a Pull, an Inner-pressure, a Push-pull, an Equi-biaxial, a Square-shape, a LT-shape and a LC-shape. Fatigue lives vary depending on the loading path when those were evaluated by the maximum Mises’ equivalent stress on inner surface of the specimen. The fatigue lives of both the steels showed a similar tendency although some Pull tests take longer fatigue life when cracks initiated from inside surface of the specimen. This study investigated the crack initiation and propagation behaviors as well as the initiation of oil leakage to prove the behavior and discusses life evaluation for two steels under wide ranged biaxial stress state, too.

Fatigue Life Properties of Stainless Steels in Wide Ranged Biaxial Stress States using a Hollow Cylinder Specimen

Stress controlled multiaxial fatigue tests were carried out using hollow cylinder specimens of type 430 and 316 stainless steels at room temperature. A newly developed fatigue testing machine which can apply push-pull loading and inner pressure to the specimen was used. For inner pressure, oil was put inside of the specimen. 7 types of cyclic loading paths were employed by combining axial and hoop stresses; a Pull, an Inner-pressure, a Push-pull, an Equi-biaxial, a Square-shape, a LT-shape and a LC-shape. Fatigue lives vary depending on the loading path when those were evaluated by the maximum Mises’ equivalent stress range on inner surface of the specimen. The fatigue lives of both the steels showed a similar tendency. However, the following difference was identified. Specifically, differences in fatigue lives of type 430 stainless steel between the uniaxial loading and the multiaxial tests were large, while those of type 316 stainless steel were small. To discuss difference in fatigue life properties between both steels, this study investigates the effect of the shear stress range, mean stress and additional hardening and which leads to evaluate the lives suitably.

Conventional triaxial compression on hollow cylinders of sandstone with various fillings: Relationship of surrounding rock with support

The interaction of surrounding rock with a support system in deep underground tunnels has attracted extensive interest from researchers. However, the effect of high axial stress on tunnel stability has not been fully considered. In this study, compression tests with and without confining pressure were conducted on solid specimens and hollow cylinder specimens filled with aluminium, lead, and polymethyl methacrylate (PMMA) to investigate the strength, deformation and failure characteristics of circular roadways subjected to high axial stress. The influence of the three-dimensional stress on the surrounding rock supported with different stiffness was studied. The results indicate that the strength and peak strain of hollow cylinders filled with PMMA are higher than those of hollow cylinders filled with aluminium or lead, indicating that flexible retaining is beneficial for roadway stability. The results obtained in this paper can contribute to better understanding the support failure of a buried roadway subjected to high axial stress and thus to analyzing and evaluating roadway stability.

Undrained monotonic and cyclic behavior of sand-ground rubber mixtures

In this study the stress–strain characteristics of sand-ground rubber mixtures are investigated in the sandlike zone, at different confining pressures, using hollow cylinder specimens subjected to torsional monotonic and cyclic loading. Under monotonic loading a mixture of sand-ground rubber with 10% and 25% rubber content show more contraction behaviour than that observed in a pure sand specimen. Phase transformation point in these mixtures are located on a larger shear strain. As expected, the shear strength of specimens decreases with increase of ground rubber content. However, with increasing of effective confining pressure, the loss in shear strength of the mixture is decreased. In addition, a mixture with 25% ground rubber shows a smaller loss in shear strength compared to a mixture with 10% ground rubber mixture. Under cyclic loading mixtures with 10% and 25% ground rubber have similar liquefaction resistance, especially at confining pressures of 110 kPa and 260 kPa. Therefore, by using of the mixture with 25% ground rubber, a larger volume of scrap tires could be recycled. The addition of ground rubber to sand would affect the shear strain variation and excess pore water pressure trends, and this effect was further intensified with increasing ground rubber percentage.

Behaviour of recycled aggregate concrete under combined compression and shear stresses

To investigate the behaviour of recycled aggregate concrete (RAC) under combined compression and shear stresses, 75 hollow cylinder specimens prepared with various replacement ratios of recycled coarse aggregate (RCA) were tested with a self-designed loading device. The results showed that the failure pattern was similar for RAC with different replacement ratios of RCA. The ultimate shear stress improved with an increasing axial compression ratio of less than 0.6 and declined after exceeding 0.6. A modified failure criterion for RAC with normal strength under combined compression and shear stresses was proposed. A new procedure to predict the shear strength for RAC beams without stirrups was developed based on the proposed failure criterion, showing a better correlation with the experimental results than the predictions calculated by GB50010, Eurocode 2, fib Model Code 2010 and ACI 318-11.

INFLUENCE OF PRINCIPAL STRESS DIRECTION ON THE STRESSSTRAIN BEHAVIOUR OF COMPLETELY DECOMPOSED GRANITE

The measurement and study of the stress-strain-strength behavior of soils in general stress states involving principal stress rotation are necessary and valuable. To investigate the strength behavior under principal stress rotation, a series of undrained tests on compacted hollow cylinder specimens of completely decomposed granite (CDG) was carried in hollow cylinder apparatus. Tests were conducted at constant inside and outside pressures and maintained a fixed angle of rotation of principal stress with the vertical (α). Seven different angles of major principal stress orientations were used to cover the entire range of major principal stress directions from vertical to the horizontal. Two different confining stresses were also used. It is observed that the deviator stresses as well as excess pore pressures decrease with the angle α. It is also observed that specimens were getting softer with the increase of α. The results also show a significant influence of principal stress direction angle on the strength parameters. It is found that the angle α is related to the occurrence of cross-anisotropy and the localization which resulted in a pronounced influence on the strength parameters of the CDG specimens.

Multiaxial fatigue properties of stainless steel under seven loading paths consisting of cyclic inner pressure and push-pull loading

The recent literature on multiaxial fatigue has reported that fatigue life evaluated by the von Mises stress is overestimated and that magnitude varies depending on the loading path. In this study, stress-controlled multiaxial fatigue tests were carried out to clarify the controlling factors in failure life using hollow cylinder specimens of type 430 and 316 stainless steel. A newly developed fatigue testing machine that can apply push-pull, reversed torsion, and inner pressure loading to the hollow cylinder specimen was employed. Seven types of cyclic loading paths, consisting of axial or hoop tension stress or a combination thereof, were employed: the Pull, the Inner pressure, the Push-pull, the Equi-biaxial, the Square-shape, the LT-shape, and the LC-shape loading paths.Since the directions of principal stresses were fixed in all the tests, all the loading paths were classified as “proportional loading.” Failure life varies depending on the loading path when evaluated by a maximum equivalent stress based on von Mises. The failure lives of the Square-shape, the LT-shape, and the Push-pull tests are overestimated significantly compared to the Pull test. A stress range that considers the directional change of shear stresses could be used to evaluate failure life. Validity was also examined by crack observation and finite element analysis.

Fatigue Testing and Evaluation of Fatigue Strength under Multiaxial Stress State; Why do we need fatigue testing?

Types of multiaxial fatigue tests and their experimental results are presented in this paper. There are typical three types in multiaxial fatigue tests: the combining push-pull and reversed torsion loading test using hollow cylinder specimen, the biaxial tension-compression test using cruciform specimen and the inner pressure applied the push-pull loading test using the hollow cylinder specimen. In the combining a push-pull loading and a reversed torsion loading test, failure life under non-proportional loading in which principal directions of stress and strain were changed in a cycle was shortened compared to proportional loading in which those are fixed. Fatigue lives were well-correlated using a non-proportional strain range considering the effect of strain path and material dependence. In the biaxial tension-compression test, the failure life decreased with increase of the principal strain ratio. In the inner pressure applied the push-pull loading test, cyclic deformation behaviour due to complex loading paths of multiaxial fatigue tests with the inner pressure associated with push-pull and rev. torsion acted to reduce the failure lives. Experimental investigation of multiaxial failure life and elucidation of their governing mechanism is essential and it can broaden the applicability of structural components.

Dynamic characteristics of expanded polystyrene composite soil under traffic loadings considering initial consolidation state

As a type of artificial filling material, the shear modulus and damping ratio of expanded polystyrene (EPS) composite soil are two key parameters used to analyze the dynamic stability of an embankment. Nineteen combined axial–torsional tests are conducted on hollow cylinder specimens of EPS composite soil to study its dynamic characteristics under the complex stress path induced by the simulated traffic loadings. The characteristics of skeleton curve, dynamic shear modulus and damping ratio for EPS composite soil are analyzed. It is found that EPS composite soil is characterized by typical dynamic nonlinearity, which is influenced by the mixing ratio and the initial stress state. The increasing cement content can effectively improve the dynamic strength of EPS composite soil. EPS bead content has a slight influence on the initial shear modulus of EPS composite soil as well as the cyclic stress-strain curve in the linear elastic stage. However, the increasing EPS bead content obviously reduces the dynamic strength. The initial shear modulus increases with increasing initial minor principal stress for the isotropic and anisotropic consolidated specimens. The characteristics of modulus attenuation are significantly influenced by the initial minor principal stress, EPS bead content and initial rotation angle of the major principal stress axis. The “structural damping” effect induced by the weak interface formed between EPS beads and cemented soil is an important component of the damping mechanism for the EPS composite soil. Based on the experimental results, this paper provides the empirical models to describe the skeleton curve, modulus attenuation and damping growth characteristics for EPS composite soil.

Influence of shear stress level on cyclic deformation behaviour of intact Wenzhou soft clay under traffic loading

Under traffic loading, the soil elements in subgrade are subjected to a cyclic cardioid-shaped stress path in the 2τvh~(σv−σh) stress plane. This significantly differs from the conventional stress paths that have been simulated using the cyclic triaxial and simple shear apparatuses, as widely reported in the literature. To date, the influence of shear stress level on cyclic deformation behaviour of intact soft clay subjected to cyclic traffic loading were rarely considered in the existing experimental investigation. For this reason, a series of cyclic hollow cylinder experiments that mimic cardioid-shaped stress paths are carried out on intact samples of Wenzhou soft clay. A wide range of vertical stress levels combined with different shear stress levels (i.e., different cardioid-shaped stress paths) are simulated in the experiments. The results show that the shear stress level significantly influences the cyclic straining and exacerbates the potential of cyclic shear failure. The difference of cyclic tests with variable shear stress level increases as the vertical cyclic stress ratio value increases. Based on the test results, an allowable cyclic stress ratio is determined to be about 0.22, which may serve as the upper bound limit of cyclic traffic loadings on soft clayey deposit. For the hollow cylinder specimens used in this study, a resilient axial strain of 3% could be a proper failure criteria value. A simplified permanent strain model that considers shear stress is proposed for the deformation behaviour of soft clay under cyclic traffic loading.

Multiaxial fatigue property of type 316 stainless steel using hollow cylinder specimen under combined pull loading and inner pressure

Stress controlled multiaxial fatigue test was carried out using a hollow cylinder specimen of type 316 stainless steel. A newly developed fatigue testing machine which can apply push-pull loading and reversed torsion loading and inner pressure to the hollow cylinder specimen was employed. 5 types of cyclic loading paths were employed by combining zero to pull axial and hoop stresses: a Pull (only axial stress), an Inner-pressure (only hoop stress), an Equi-biaxial (equi-biaxial stress by axial and hoop stresses), a Square-shape (trapezoidal waveforms of axial and hoop stresses with 90-degree phase difference) and a L-shape (alternately axial stress and hoop stress) loading paths. Since directions of principal stresses are fixed in all the tests, all of the loading paths are classified into ‘proportional loading’. In the Pull, the Inner-pressure and the Equi-biaxial tests, fatigue lives can be correlated on a unique line by a maximum equivalent stress based on von Mises. On the other hand, fatigue lives in the Square-shape and the L-shape tests were reduced comparing with that in the other tests, which was caused by yielding of larger plastic deformation.